>For what it's worth, the processes I've tested or seen tested -- Vandyke
>brown, kallitype and cyanotype -- all do much better, that is, better
>d-max, better tone separation, airdried without heat.
>
>As I mentioned a while back, you don't need a size for VDB if you airdry
>without heat, and there is much less random bronzing of the shadows.
Bronzing in VDB and Kallitype as well as the traditonal platinum process is
due to the emulsion not being >>in<< the surface of the paper, but rather
being >>on<< the surface. A secondary but related condition is too thin of
a coating. In the Bath APIS last year Mike Ware showed some electron
microscope prints of the paper fibers with and without the use of Tween20.
With Tween20 the metal was actually in the fibers, the fibers being hollow
tubes, and the metal particles were inside the tube itself. They were
stunning pictures and very revelatory.
With over a year and a half's experience with the Ziatype it is my opinion
that one cannot make any universal claims about airdrying and forced heat
drying. (Judy is only citing her experience and not making any univesal
claim.) Much of this depends on the local climatic conditions. Two days ago
it was 88 degrees and 8% humidity here in Santa Fe. I'd usually pick Key
West as the opposing climate but right now it seems that they may be
enjoying a Santa Fe climate there as well.
If it is extremely humid, your prints may never dry, so some heat will be
necessary. If it is 8% humidity and you are at 7000 foot altitude -- (some
say we live in a near vacuum, but that leads to all kinds of humorous
asides), but if you are at 8%, measures must be taken to allow some "sink
time" for you emulsion. Too dry an atmosphere leads to what Carl Weese and
I refer to as the "cold snap syndrome." Running the paper over a
electrostatic humidifier for a minute seems to work miracles in platinum
printing, and I'd expect the same for the other metal processes ... maybe
even gum.
--Dick Sullivan